Edible oils have been refined from ancient times. Since the emergence of the fast food industry, the refining of edible oils has been extended to rejuvinating, refreshing and preserving used cooking oil. Also, the types of oil used in the fast food industry have expanded from animal fats to include vegetable oils, such as soybean, cottonseed, or palm oil.
In order to effectively treat the principal contaminating factors of used cooking oil, it is desirable to remove food particles, remove phospholipids, deodorize the oil and decolor the oil. A number of different processes have been developed for treating used cooking oil, but none of the processes to date have been sufficiently effective in treating all of the defects of the used cooking oil. It is an object of the present invention to provide a filter material which is effective in treating all of the principle contaminating factors of used cooking oil.
The art has several methods of treating used cooking oil which have the effect of reducing the production of soap. U.S. Pat. No. 4,764,384 of John Gyann entitled METHOD OF FILTERING SPENT COOKING OIL adsorbs free fatty acids by treating used cooking oil with a composition of silicates including a hydrated amorphous silica gel, thereby reducing the combination of free fatty acids and metallic ions and the resulting soap. Another approach to controlling the concentration of free fatty acids by adsorption is described in U.S. Pat. No. 4,235,795 of Cohen, and this approach admixes pumicite with used cooking oil as an adsorbent for free fatty acids. A third method of treating used cooking oil to reduce soap is described in U.S. Pat. No. 4,330,564 of Friedman in which a chelating agent is admixed with the cooking oil to tie up the metal ions and prevent the combination of free fatty acids and metal ions and the resulting production of soap. Another method of treating used cooking oil to prevent soap is described in U.S. Pat. No. 3,231,390 of Hoover in which used cooking oil is treated with an adsorbent consisting of an alkaline earth metal carbonate or an alkaline earth metal oxide, and the adsorbent is removed from the oil by filtration. It is believed that the process of Hoover is a saponification process which removes the metallic ions as soap in the filtration step.
These processes are effective in preventing the formation of soap and filtering food particles from the used cooking oil, but these processes do not decolor the used oil. Cooking oil is maintained at an elevated temperature during the cooking process, a temperature of about 300 to 400 degrees Fahrenheit. The elevated temperature and the presence of food juices and particles causes the oil to gradually darken in color until it reaches a dark brown color. It is generally believed that the dark brown color is a precursor to rancidity, and it may cause the oil to be discarded before it becomes too contaminated for continued use.
Further, filter media differ in their effect on the taste and odor of products cooked in used and filtered cooking oil. The products pick-up the odor of the cooking oil and taste from the cooking oil. Hence it is a further object of the present invention to provide a filter media which excels in deodorizing used cooking oil and which imparts a superior flavor to products cooked with used cooking oil which has been filtered with that filter media.
It is also an object of the present invention to provide a filter media useful in the refining of raw glyceride oil. While raw glyceride oil is not subjected to crumbs and juices from cooking food, free fatty acids must be refined from such oil. Further, deodorization, decolorization, removing phospholipids, soap, and oxydized matter are important in the processes of refining such oils.